Dynamic responses of a kinetic energy projectile under transverse loadings

We report on the effects of launch tube nonstraightness and asymmetric loading on the accuracy performance of a kinetic energy projectile. Modeling the projectile as a rigid body within the launch tube, we obtain and solve the equations of rotary motion to calculate the orientation of the projectile relative to the tube as a function of time. Three launch tube geometries are modeled; curiously, the most severe environment does not produce the most deviant projectile orientations during in-bore travel or at muzzle exit. To determine the effects of asymmetric loading, we model the rod as a nonuniform two-dimensional beam, subject to a transverse blast load. Determined experimentally, the sabot equivalent stiffness is bounded between 10⁶ and 10⁷ N/m. These bounds are used in an elastic boundary condition to the rod finite element model. The ANSYS transient vibration analyses predict a peak transverse displacement of 20 mm and a peak transverse velocity of 75mm/s at muzzle exit. We conclude that: (1) base pressures asymmetry induces transverse vibrations in the projectile, and these vibrations are affected by sabot stiffness; and (2) launch tube profile nonstraightness induces rigid body rotations in the projectile, and these rotations may or may not increase with launch tube severity.     

Large-scale,hypervelocity, high-fidelity interceptor lethality development in AEDC's range G

The hypervelocity ballistic range G at the Arnold Engineering Development Center (AEDC) is extensively used to conduct kinetic energy lethality tests for the Missile Defense Agency (MDA). Over the years, AEDC has continuously responded to the lethality test and evaluation requirements of Ballistic Missile Defense Systems (BMDS) at hypervelocity intercept conditions. Projectiles launched from two-stage light-gas guns experience acceleration loads that are typically orders of magnitude greater than those of the actual missile defense system. These acceleration loads drive design compromises in the projectiles' geometry and mass–density distribution necessary to survive the launch environment. A “high-fidelity” projectile with the proper geometry and mass–density distribution would provide a more representative simulation of the flight vehicle kinetic energy release at impact. Prior to the current upgrades, the range G facility provided the capability to launch large projectiles [8-in. (203-mm) diameter] with weights up to 12 kg at launch velocities up to 4 km/s but at acceleration loads near 40 K g's. Current upgrades provide for the capability to launch large-scale “higher fidelity” projectiles at the same high velocities but at half the g loads. In addition, AEDC is developing a new technique for controlling the projectile pitch at the point of impact with a simulated target. These unique capabilities will make it possible to obtain more flight-representative lethality data in a ballistic range. This paper describes the upgraded capabilities now in place and continuing plans for further upgrades.     

Modeling and reduction of shocks on electronic components within a projectile

Electronic components within a projectile are subjected to severe loads over an extremely short duration during the launch process. Failure of these components during launch can result in negative effects on the mission of the projectile. While experimental data can be helpful in understanding failure of electronic components within a projectile, collecting such data are usually difficult. There are also limitations on the reliability of sensors under these circumstances. Finite element modeling (FEM) can offer a means to better understand the behavior of these components. It can also be used to develop better shock mitigation features into the projectile design. This research has two objectives. The first objective is to develop an FEM that one describes the interaction of a typical projectile with the gun barrel during launch. The projectile includes a payload of a one-pound mass representing a typical electronic package supported by a plate. The second objective of this work is to investigate the use of composite plates to support electronic payload as a means to reduce the transmitted shocks during the projectile launch event. The proposed plate has carbon fibers embedded in an epoxy matrix. A parametric study of the effects of varying the thickness of the supporting plate and the fiber volume fraction on the accelerations and stresses is included. Results of the study are used to reach general recommendations regarding reducing failure of electronic components within a projectile.     

The DES raligun facility at CEM-UT

The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has constructed a facility for the operation of electromagnetic (EM) launcher experiments. The facility was specifically designed to investigate distributed-energy-store (DES) railguns. Experiments conducted in the facility have demonstrated the DES railgun concept using a 1-m long, four-stage DES railgun. Investigations have begun on a 4-m, ten-stage DES railgun to demonstrate operation of such a system at higher projectile velocities. The capabilities and design of the major components of the facility are described. Also presented is a review of the experimental development of the railgun system. The DES railgun facility is a versatile laboratory test bed facility for EM acceleration experiments.     

串联发射弹丸内弹道力学特性测试方法研究

针对小口径高射频串联发射弹丸的内弹道力学特性测试问题,提出了基于弹载存储测试技术的弹底压力、弹前压力同步测试方法。设计了模拟弹和小型聚偏二氟乙烯(polyvinylidene difluoride, PVDF)压电式力传感器,将力传感器作为底螺与头螺部件承受并测量弹底压力与弹前压力,在发射过载条件下进行了传感器力学分析并推导了受力与输出的关系方程;分析了传力块的质量、厚度,PVDF薄膜的厚度、面积对传感器动态特性和温升的影响;进行了力传感器灵敏度理论建模与分析并开展了标定试验。结果表明,PVDF薄膜预紧力越大,传感器灵敏度越小。开展了串联发射试验,测试结果和内弹道数值模拟计算结果吻合较好。     

Time-resolved penetration of long rods into steel targets

The penetration behavior of tungsten alloy, long-rod penetrators into high-hard steel is investigated at two impact velocities; 1.25 km/s and 1.70 km/s. The positions of the nose and tail of the projectile were measured by means of a 600 kV flash X-ray system at different times during penetration. The wavecode CTH was used to numerically simulate the experiments. The computational results are in very good agreement with the experimental position-time data. Additionally, the computational model reproduces the qualitative behavior for impact conditions near the ballistic limit.     

Particle launch to 19 km/s for micro-meteoroid simulation using enhanced three-stage light gas gun hypervelocity launcher techniques

Particle launch experiments were performed to study application of the enhanced hypervelocity launcher (EHVL), i.e. the third-stage addition to the two-stage gun, for launching micron to millimeter sized particulates at velocities unobtainable with a standard two-stage light gas gun launch. Three types of particles or fliers were tested along with several barrel designs. For micron scale particles fine-grain polycrystalline ceramics were impacted and fractured, launching particulate clouds at velocities of 15 km/s. Multiple titanium particles 400 μm diameter embedded in plastic were “shotgun” launched to velocities of 10 km/s. Flier plates of 3 mm diameter by 1 mm thick Ti6Al4V were launched to 19 km/s. All experiments used a second-stage projectile with graded density facing impacting a flier in an impact generated acceleration reservoir. This paper describes the modification and adaptation of the Sandia EHVL to provide micrometeoroid simulation capabilities.     

Electromagnetic gun/projectile interface considerations

Projectile/electromagnetic-gun interface design considerations for electromagnetic gun weapon system (EMGWS) area D1 projectiles, area B-guns, and area C-guns are presented. Projectile/EM gun interfaces are primary considerations in the projectile structural design and the design of the sabot obturator/bore rider, pusher plate, and armature. Acceleration profile, armature type and mass, preinjector characteristics, bore pressure, magnetic fields, and plasma temperature are all key issues in the ultimate projectile performance. Armature design is a critical technical issue for both the projectile and EM gun design because of the high masses involved. Solid armatures are heavier than plasma armatures, but operate at higher electrical efficiencies. Plasma armatures are both being considered for the B-guns and C-guns. Performance tradeoffs are presented for penetration versus peak acceleration and armature mass. Contributors to projectile dispersion such as in-bore balloting, projectile spin, and EM launcher muzzle arc effects are assessed     

Multiphysics modelling of the coupled behaviour of precision-guided projectiles subjected to intense shock loads

Precision-guided projectiles (PGPs) typically deployed in smart munitions are operated and guided by highly sophisticated embedded electronic systems (EES). These PGPs are subjected to severe shock loads resulting from the ignition of the propellant during their launch. These shock loads, which are typically characterised by high intensity, short duration and wave reflections at varied frequencies, often lead to the failure of the EES. It is the objective of this work to conduct a comprehensive multiphysics analysis of the launch process of PGPs accounting for coupling and interaction effects between the different media (propellant, PGP, confined volume and free space). Specifically, we investigated the entire launch process that include the ignition of the propellant to observe local and global features of the setback, set forward pressure and acceleration histories using explicit axisymmetric Lagrangian–Eulerian finite element simulations. In this work, we also examine the severity and frequency of the reflected waves as well as the springback of the PGPs resulting from these local oscillations as they exit the muzzle. In addition, the flight state transition due to muzzle exit in terms of pressure and flow velocity is also discussed. Our results reveal the complex phenomena associated with the dynamic response of the PGPs and pressurization process resulting from the ignition of propellant during launch that are characterized by high oscillatory pressure profiles and projectile springback.     

Soft acceleration of a metal plate by a rail gun plasma

The following situation is considered: A dense plasma armature which has been accelerated to a high velocity in a rail gun is allowed to impact a stationary metal plate. At impact, a shock wave is transmitted into the plate and a shock wave is reflected back into the plasma. For very high plasma velocities, the subsequent behavior depends primarily on the plasma density profile just prior to impact. The appropriate partial differential equations are analyzed in plane geometry and the conditions required to prevent spallation of the plate are determined. These results are compared with the "plasma only" armature plasma profiles predicted by Sloan, and it is shown that the conditions for not spalling the metal are well satisfied. The typical rail gun makes use of a low mass plasma armature to continuously accelerate a more massive solid projectile down the length of the rails. It has been suggested that substantially higher velocities and energies may be achievable with a "plasma only" rail gun-which has no solid projectile, but which has an armature mass comparable to the mass of a solid projectile. Subsequent to the acceleration, the momentum of this high velocity plasma must be transferred to a solid projectile. One way to do this is to simply allow the plasma to collide with the projectile. For this to be of interest, the projectile should not shatter and the energy transfer should be reasonably efficient. The purpose of the paper is to analyze an idealized model of such a collision.     

Experimental results from CEM-UT's single shot 9 MJ railgun

A 10-m-long, 90-mm bore railgun has been designed and fabricated. During the test program, a number of solid armatures and projectile packages have been tested in a 50-m-deep vertical test range. The experiments are powered by six homopolar generator (HPG) charged inductive stores, sequentially staged to provide the desired acceleration profile. Prior to testing, computer simulations are run to determine the preferred current profile and predict system performance. During projectile flight, high-speed films, X-rays, muzzle volts, and velocity/acceleration profiles are recorded along with power supply operating parameters. Postshot diagnostics include bore wear analysis and armature and target recovery. Comparisons of predicted and recorded shot performance are also made. On selected tests, an energy balance is performed to determine efficiencies of the various components. A summary of all 90-mm gun shots is presented along the critical data collected from selected tests     

The ballistic performance of SiC–AA7075 functionally graded composite produced by powder metallurgy

The potential of silicon carbide reinforced Functionally Gradient Material (FGM) to be used as armor material was investigated under the impact of armor piercing projectile. For this purpose, the SiC–Aluminum Alloy (AA) 7075 functionally graded composite at different thicknesses was produced from the metallic and ceramic powders via powder metallurgy method. Before the ballistic testing, the precipitation hardening behavior of the samples was determined. And also, the microstructural characterizations of the samples were done with the aid of microscopy techniques. Next, the FGM samples were tested using armor piercing projectile to analyze their impact behavior. In the produced samples, some pore formation was detected. The ballistic experiments showed that the investigated FGMs (up to a thickness of 25 mm) did not withstand the impact of the projectile. At the tested samples, some major cracks and plug formation were detected at macrolevel while there were some microcracks, deformed and elongated grains in the regions near to the deformation zone of the samples.     

The electromagnetic θ gun and tubular projectiles

Unlike the better known rail gun, the θ gun applies the propelling force along the length of its projectile. This is shown to allow much greater acceleration of high fineness ratio projectiles for a given barrel pressure, allowing much shorter barrels for military applications. A computer code which simulates performance of the θ gun is described and experimental results from a few simple, low energy experiments show close agreement with code predictions. Trajectories and aerodynamic heating for three candidate military projectiles are calculated for vertical and horizontal atmospheric launches where initial velocity is as high as 3 km/s. The calculations indicate that in some cases a thin layer of heatshield (ablator) will be required to control projectile heating.     

考虑身管柔性的坦克行进间发射动力学研究

针对弹丸起始扰动会影响坦克行进间射击密集度问题,建立身管柔性的坦克行进间发射动力学模型;考虑弹丸动不平衡及质量偏心、弹炮相互作用、弹炮间隙,建立坦克行进间射击弹丸膛内运动方程;编制行进间射击的坦克发射动力学仿真程序,获得某坦克行进间射击弹丸膛内运动规律及千米立靶密集度,并试验验证仿真结果。该结果可为提高坦克行进间射击精度提供理论基础与仿真手段。     

多管火箭发射过程中定向器振动特性研究

为了在多管火箭发射过程中能获得准确的定向器管口振动特性,本文研究多管火箭发射过程中定向器管口振动特性;利用多体系统传递矩阵法和发射动力学理论,建立了多管火箭发射动力学模型和仿真系统,通过多管火箭模态试验验证了模型的正确性;仿真获得了在发射过程中定向器管口振动的时域历程,利用离散傅里叶变换(DFT)技术,获得了在发射过程中定向器管口振动位移、速度和加速度信号的频域特性;在此基础上设计了椭圆滤波器,并通过对发射过程中定向器管口的加速度采集信号的滤波前后对比,验证了本文研究内容的正确性和重要性,为多管火箭发射过程中定向器运动信号的采集和控制提供了重要参考价值。     

蜂窝铝的侵彻实验研究与有限元模拟

目的 研究弹体侵彻蜂窝铝的力学行为。方法 在实验中, 通过轻气炮加速的尼龙弹体冲击蜂窝铝靶体。利用Ansys/LS-DYNA建立了弹体侵彻蜂窝铝的壳单元有限元模型。结果 实验给出了冲击速度为140和167 m/s时弹体的加速度曲线。运用壳单元模型对蜂窝铝的侵彻进行模拟, 得到了弹体的加速度曲线以及蜂窝铝在侵彻过程中的变形图。结论 将模拟结果与实验结果进行了对比, 发现模拟结果与实验结果符合较好, 证明了壳单元有限元模型模拟蜂窝铝侵彻行为的可靠性。     

Experimental impacts above 10 km/s

In the proceedings of the last symposium, recent work on a technique for launching small projectiles to hypervelocities above 10 km/s using an inhibited shaped charge was presented [1]. In the interim, experiments have been conducted using the inhibited shaped charge to launch aluminum, nickel, and molybdenum projectiles. This paper presents the results of the impact tests, as well as discusses the shaped charge design modifications for the nickel and molybdenum launchers. Radiographs are presented of the impacting projectiles, as are post test photographs of various targets. The data are unique in that they represent low L/D projectile impacts into both monolithic blocks and spaced plates at velocities above 10 km/s. The aluminum projectiles are being launched at 11.25±0.20 km/s, the molybdenum projectiles at 11.72±0.10 km/s, and the nickel projectiles at 10.81±0.10 km/s.     

应力波传播对弹丸实测超高值加速度的影响

采用较为简单的力学模型和简化的边界条件,以直杆一端施加一半正弦载荷脉冲和模拟弹体冲击刚性靶为例,用理论推导和计算机仿真的方法分析应力波传播和弹体加速度的关系.并采用LS-DYNA对加速度存储测试电路系统(含其缓冲结构)的壳体上不同点的加速度分布进行了计算机仿真.研究表明,在弹体侵彻目标时,刚体的弹体质心加速度与实际值相差好几倍,数据处理时应根据具体目的分析.     

A new analytical model of normal penetration of projectiles into the light-weight ceramic–metal targets

In this paper based on Zaera and Sanchez-Galvez [4] model, a new analytical model has been presented for penetration of deformable projectiles into ceramic–metal targets. By considering erosion and flattening of projectile tip, the one-dimensional equation of motion has been established. The momentum equation has been employed to describe the fragmented ceramic conoid. Considering work hardening material behavior, energy conservation equation has also been used for modeling the deformation of back-up metallic plate. Semi-angle of ceramic conoid is modified based on Wilson and Hetherington [8] experiments. The ballistic limit and residual velocity of projectile predicted by new analytical model have a good agreement with the experimental results.     

An examination of deviations from hydrodynamic penetration theory

The hydrodynamic theory of penetration (HTP) was first developed in the U.S. during WWII, and independently and essentially simultaneously in England. Since then the theory has proved very useful in understanding and predicting results of many penetration experiments. The assumptions and limitations of HTP were well stated in the initial paper. The most obvious limitation is that, strictly speaking, HTP only applies to hydrodynamic materials, i.e., both the projectile and the target have no strength. But for nearly all cases of interest, penetration does depend on material strengths, even at quite high velocities. Consequently, effects of projectile and target strength on penetration physics have been studied by many researchers, and modified versions of HTP have been proposed. While material strength is an important reason for deviations from HTP, it is not the only one. Other assumptions underlying HTP are steady-state behavior and incompressibility. In this paper we present new numerical simulation results that examine and quantify deviations from HTP due to compressibility for several material combinations of interest as a function of impact velocity. For these calculations all the materials are modeled as having zero strength. This is done in order to separate effects of compressibility from effects due to material strength. Some discussion of transient effects is also provided.